JP6691811B2 - Plugged honeycomb structure and method for forming plugged honeycomb structure - Google Patents

Description

  The present invention relates to a plugged honeycomb structure and a method for forming the plugged honeycomb structure. More specifically, a plugging portion used for an exhaust gas purifying device or a collecting filter for collecting and removing particulate matter contained in a fluid such as exhaust gas discharged from a diesel engine, etc. The present invention relates to a plugged honeycomb structure and a method for forming the plugged honeycomb structure.

  Exhaust gas (fluid) discharged from an automobile diesel engine or the like contains a large amount of various particulate substances such as dust, soot, and carbon fine particles. Release of these particulates into the atmosphere can have a large impact on the natural environment. Therefore, direct release of exhaust gas and the like into the atmosphere is restricted by various laws and regulations. Therefore, a purification process using an exhaust gas purification device, a collection filter, etc. is performed before the emission.

  The exhaust gas purifying apparatus or the like used in the purification treatment includes a honeycomb base material made of ceramics, which has partition walls extending from one end surface to the other end surface and in which a plurality of cells forming a fluid passage are partitioned and formed. Generally, a plugged honeycomb structure including a plugged portion in which cells on each end surface of the honeycomb substrate are plugged according to a predetermined arrangement standard is used (for example, Patent Document 1). reference.).

  Exhaust gas containing particulate matter flows from one end face of the plugged honeycomb structure into the inside thereof, and passes through the partition walls formed of a porous ceramic material, so that The particulate matter is collected. As a result, the purified purified gas discharged from the other end surface of the plugged honeycomb structure is in a state in which the particulate matter contained in the original exhaust gas is removed.

  A fluid such as exhaust gas is promptly guided to an exhaust gas purification processing device or the like directly connected to an exhaust system of a diesel engine or the like. Therefore, the fluid immediately after being discharged from a diesel engine or the like is often in a high temperature state. Therefore, the plugged honeycomb structure has excellent thermal properties such as heat resistance and thermal shock resistance so as to withstand thermal shock even when exposed to a high temperature fluid for a long time. It is necessary to have, and mainly ceramic materials are used.

  For example, as a raw material forming a plugged honeycomb structure (mainly partition walls), a particulate base material (also called an aggregate) and a particulate base material in which pores are formed A ceramic material including a bonding material for bonding the base materials is used. More specifically, silicon carbide, silicon nitride, or the like is used as the base material (aggregate), while crystalline and porous cordierite is used as the binder, and further, in a partial configuration of the binder, A material containing a rare earth element or a zirconium element has been proposed (see, for example, Patent Document 2).

JP, 2003-254034, A JP, 2005-67473, A

  Using an exhaust gas purification treatment device or the like that employs a plugged honeycomb structure as described above, when performing a purification treatment on a fluid, inside the cells of the plugged honeycomb structure, the collected soot and the like A large amount of particulate matter is deposited. Here, as described above, the plugged honeycomb structure is provided with a plurality of plugging portions according to the arrangement standard previously defined for each cell on one end face and the other end face. ..

  Therefore, in comparison with one end surface (inflow side end surface) of the plugged honeycomb structure on the fluid inflow side (inlet side), the other end surface (discharge side end surface) of the fluid discharge side (outlet side) is The plugging portion particularly restricts the flow of fluid. As a result, there was a strong tendency that a large amount of particulate matter was deposited inside the cell on the upstream side of the cell provided with the plugged portion.

  Therefore, a regeneration treatment is generally performed in which a high-temperature gas fluid is forcibly introduced into the plugged honeycomb structure in which the particulate matter is deposited to remove the particulate matter deposited in the cells. Here, as described above, the particulate matter is often dust, soot, carbon fine particles, or the like. As a result, when the high temperature gas fluid containing oxygen and the particulate matter are brought into contact with each other, the oxygen in the atmosphere and the particulate matter are bonded to generate carbon dioxide. That is, by the above regeneration treatment, the solid particulate matter is gasified into carbon dioxide and discharged from the other end surface, so that the particulate matter can be relatively easily removed from the inside of the cells of the plugged honeycomb structure. Therefore, the particulate matter can be easily restored to the state before the collection.

  The regeneration treatment can be performed regularly at a frequency or cycle defined in advance, or can be appropriately performed depending on the amount of particulate matter deposited inside the cell. This prevents cracks and the like from occurring in the plugged honeycomb structure during the regeneration process, which adversely affects the performance of collecting particulate matter, and can prolong the life of the plugged honeycomb structure. ..

  However, in the regenerating treatment, the high temperature gas fluid is forced to flow into the inside of the plugged honeycomb structure, which may cause the following problems. That is, a large amount of energy cost may be required in order to generate a high temperature gas fluid that is introduced to gasify the particulate matter. In this case, it is possible to generate a high temperature gas fluid from the diesel engine by controlling the rotation speed of the diesel engine or by injecting fuel directly into the pipe for regeneration processing. This resulted in the consumption of more fuel compared to normal diesel engine operation.

  Here, in order not to cause cracks or the like in the plugged honeycomb structure, increasing the frequency of the above-mentioned regeneration treatment and performing it frequently results in a large fuel consumption, and the fuel consumption performance of the entire operation of the diesel engine or the like is remarkably high. It could be reduced. In addition, even in the process of converting particulate matter such as soot into carbon dioxide and discharging it into the atmosphere, it emits carbon dioxide, which is one of the factors contributing to global warming, so it is less preferable from the effect on the natural environment. Was not.

  Therefore, in order to reduce the amount of carbon dioxide emission while suppressing fuel consumption and maintaining high fuel efficiency, the number of times of regeneration treatment performed on the plugged honeycomb structure is reduced as much as possible. Was desired.

  However, the decrease in the number of times of the regeneration treatment inevitably increases the amount of particulate matter deposited inside the cells of the plugged honeycomb structure. In this state, when a high temperature gas fluid is caused to flow into the plugged honeycomb structure, a large amount of particulate matter is deposited, for example, the amount of heat near the upstream position of the plugging portion provided on the discharge side end face is locally generated. It sometimes becomes extremely large and becomes extremely hot. As a result, the thermal stress applied to the plugged honeycomb structure was increased, the thermal stress could not be withheld, and cracks and the like were more likely to occur at the partition wall intersections of the cells. This causes a problem such as damage to the plugged honeycomb structure.

  Further, as the amount of heat locally applied to the plugged honeycomb structure increases, an excessive amount of particulate matter may be deposited, which may increase the temperature of the entire plugged honeycomb structure. This may cause a problem that the raw material forming the partition walls of the plugged honeycomb structure reaches a temperature equal to or higher than the melting point, and some partition walls of the plugged honeycomb structure are melted and damaged.

  Therefore, in view of the above situation, the present invention suppresses and relaxes the concentration of locally applied thermal stress, and can suppress the amount of cracks generated inside the cells, and the plugged honeycomb structure. It is an object to provide a method for forming a body.

  According to the present invention, there is provided a plugged honeycomb structure that solves the above problems, and a method for forming a plugged honeycomb structure.

[1] A honeycomb substrate having porous partition walls extending from one end face to the other end face and partitioning and forming a plurality of cells serving as fluid channels, and the cells on the one end face of the honeycomb substrate. While plugging according to a predetermined disposition standard, a plugging portion that plugs each of the remaining cells in the other end surface is provided, and from the inflow side end surface that is the one end surface of the honeycomb substrate. A plugged honeycomb structure for collecting particulate matter contained in the fluid flowing toward the discharge side end surface which is the other end surface, wherein the partition wall is a particulate base material, and the base. The materials are bound to each other and contain a binder having a lower melting point than the base material as a raw material, and the particle diameter of the base material is in the range of 5 μm to 60 μm, and the total mass of the base material and the raw material containing the binder is Said binding to The mass ratio of the cells is in the range of 22% by mass to 45% by mass, and the cells are partitioned and formed into a circular shape, an elliptical shape, or a semicircular shape by an arc partition wall in which at least a part of the partition wall has an arc shape. been possess a part circular cell, the radius of curvature at partition wall intersection points of the circular arc partition walls forming, by surrounding the circular cell, plugged honeycomb structure is 250μm or more.

[2] The ratio of the number of circular cells of the circular cells to the total number of cells of the orthogonal cells orthogonal to the honeycomb axis direction of the plugged honeycomb structure is 10% or more. Plugged honeycomb structure.

[3] The plugged honeycomb structure according to the above [1] or [2], wherein the circular cells are positioned in proximity to the plugged portions provided on the discharge-side end surface.

[4] Injecting the fluid from the inflow side end surface of the polygonal plugged honeycomb structure before capturing the particulate matter, which has a plurality of polygonal polygonal cells partitioned by the partition walls, Any one of the above [1] to [3] having the circular cells formed by deforming the polygonal cells by exposing the binder to a temperature equal to or higher than a melting point after collecting the particulate matter. The plugged honeycomb structure described.

[ 5 ] The plugged honeycomb structure according to any one of [1] to [ 4 ], wherein the binder has a melting point of 1100 ° C. or higher.

[ 6 ] The base material and the binder are one or more ceramic materials selected from the group including cordierite, alumina, mullite, silicon nitride, silicon carbide, and aluminum titanate. [1] to [ 5 ] ] The plugged honeycomb structure according to any one of [1] to [4].

[ 7 ] The plugged honeycomb structure according to the above [ 6 ], wherein the base material is the silicon carbide, and the binder is the cordierite.

[ 8 ] The method for forming a plugged honeycomb structure according to any one of [1] to [ 7 ], wherein a plurality of polygons extending from one end face to the other end face and serving as fluid passages are formed. A honeycomb base material having a porous partition wall that defines cells, and plugging the polygonal cells on the one end surface of the honeycomb base material according to a predetermined disposition standard, and a residue on the other end surface. For a polygonal plugged honeycomb structure having plugged portions respectively plugging the polygonal cells, from the inflow side end face that is the one end face to the discharge side end face that is the other end face. A fluid inflow step of inflowing the fluid, and a particulate matter for depositing and collecting particulate matter contained in the fluid inside the cells of the polygonal cell having the plugging portion formed on the discharge side end face. A material collection process, After the particulate matter is deposited inside the cell by the particulate matter collecting step, the polygonal plugged honeycomb structure is exposed to a temperature equal to or higher than the melting point of the binder, whereby the polygonal cell A plugged honeycomb structure having at least a part of which is a circular cell deforming step in which the partition wall is deformed into an arc partition wall having an arc shape and is transformed into a circular cell having a circular shape, an elliptical shape, or a semicircular shape. How to form a body.

  According to the plugged honeycomb structure of the present invention and the method of forming the plugged honeycomb structure, the circular cells are included in a part of the cells at a predetermined ratio, so that the cells are added to the inside of the plugged honeycomb structure. It is possible to disperse the thermal stress concentration at the time of collecting the particulate matter and suppress the local application of the thermal stress to the partition wall intersections and the like. This makes it possible to suppress the number of occurrence of cracks and the like while maintaining the strength of the plugged honeycomb structure inside the plugged honeycomb structure.

In particular, compared with one in which a part of the cells is configured by circular cells in advance, a conventional polygonal plugged honeycomb structure configured by polygonal cells is prepared, and then particles are added to the polygonal plugged honeycomb structure. By flowing a fluid containing particulate matter to form a circular cell, it is possible to prevent a decrease in cell density and an increase in pressure loss at the beginning of collection. Furthermore, using a binding material having a low melting point relative to the substrate, by appropriately adjust the weight ratio of the particle size and binder substrate, formed of a circular cell during reproduction processing after collecting the particulate matter Will be easier.

FIG. 1 is a perspective view schematically showing a schematic configuration of a plugged honeycomb structure of one embodiment of the present invention. It is explanatory drawing which shows typically the state of the base material in a partition, and the binding material which couple | bonds the said base materials. FIG. 3 is a cross-sectional view showing a schematic configuration of a polygonal plugged honeycomb structure before collecting particulate matter. FIG. 3 is a cross-sectional view showing a schematic configuration of a plugged honeycomb structure of the present embodiment in which circular cells are formed after collecting particulate matter. FIG. 5 is an enlarged cross-sectional view schematically showing a section taken along the line CF-CF in FIG. 4 inside a cell adjacent to the other end surface side of the plugged honeycomb structure.

  Hereinafter, the plugged honeycomb structure and the method for forming the plugged honeycomb structure of the present invention will be described in detail with reference to the drawings. The plugged honeycomb structure of the present invention and the method for forming the plugged honeycomb structure are not limited to the following embodiments, and various designs are possible without departing from the gist of the present invention. Changes, corrections, and improvements can be made.

1. Plugged honeycomb structure
As shown in FIGS. 1 to 5, the plugged honeycomb structure 1 of the present embodiment has a substantially columnar shape, and one end face 2a (inflow side end face 3a of the plugged honeycomb structure 1) to the other end face 2a. A plurality of flow paths extending to the end surface 2b of the plug (exhaust-side end surface 3b of the plugged honeycomb structure 1) such as an exhaust gas containing particulate matter 10 (see arrows in FIGS. 1 and 3 and 4). The honeycomb base material 6 having partition walls 5 made of a porous ceramics material for partitioning and forming the cells 4 and the openings 7a of the cells 4 on one end face 2a of the honeycomb base material 6 are provided as predetermined arrangement standards. And the plugging portions 8 in which the openings 7b of the remaining cells 4 on the other end face 2b are plugged respectively.

  In the plugged honeycomb structure 1 of the present embodiment, at least some of the cells 4 are circular cells 9 which are partitioned and formed in a circular shape, an elliptical shape, or a semicircular shape by an arc partition wall 5a having an arc shape. .. Here, the circular cells 9 cannot directly visually recognize the shape from the inflow side end surface 3a and the discharge side end surface 3b of the plugged honeycomb structure 1, and the honeycomb axial direction A of the plugged honeycomb structure 1 ( It becomes visible by cutting at an orthogonal plane CF (see a virtual cut plane surrounded by a chain double-dashed line in FIG. 1 or a cross section taken along the line CF-CF in FIG. 4) orthogonal to the one-dot chain line in FIG. 1). Is. That is, in the plugged honeycomb structure 1 of the present embodiment, the circular cells 9 are present inside. On the other hand, each cell 4 of the inflow side end surface 3a (one end surface 2a) and the discharge side end surface 3b (the other end surface 2b) has a polygonal shape (square shape in the present embodiment).

  Furthermore, in the plugged honeycomb structure 1 of the present embodiment, the ratio of the number of circular cells 9 (the number of circular cells) to the total number of cells 4 in the orthogonal plane CF (corresponding to a virtual cut surface) is 10%. It is set as described above. In order to enjoy the effect of relaxing the thermal stress concentration by the circular cells 9 (details will be described later), a certain number or more of circular cells 9 must be present with respect to the total number of cells 4 in the orthogonal plane CF. Because there is.

  The positions of the circular cells 9 in the plugged honeycomb structure 1 are not limited to those in the above embodiment, and can be formed at any position along the honeycomb axial direction A. Therefore, the circular cells 9 are formed in the openings 7a and 7b of the cells 4 on the one end surface 2a or the other end surface 2b of the honeycomb substrate 6 where the plugged portions 8 are not provided, and the plugged honeycomb structure is obtained. It may be directly visible from the outside of the body 1.

  However, from the viewpoint of the method for forming the circular cells 9 described later and the effect based on the circular cells 9, as in the plugged honeycomb structure 1 of the present embodiment, the inside of the plugged honeycomb structure 1, particularly the discharge. It is particularly suitable to form it by being distributed at an upstream position close to the side end surface 3b.

  In the plugged honeycomb structure 1 of the present embodiment, the plugging portion 8 that plugs the cells 4 is the same well-known plugging portion used in the conventional plugged honeycomb structure. Can be used. Here, in the plugged honeycomb structure 1 of the present embodiment, one opening is formed by alternately plugging the openings 7a of the cells 4 on one end surface 2a alternately with each other, and further the one step is formed. The positions of the plugging portions 8 in the upper and lower rows are shifted to the left and right one by one and alternately plugged, so that a plurality of plugging portions 8 are arranged in a checkerboard pattern (checkerboard pattern). (See FIG. 1, etc.).

  Similarly, with respect to the remaining cells 4 on the other end surface 2b of the honeycomb base material 6, the grid-like plugging portions 8 are similarly arranged while alternately shifting the position of every other cell 4. Here, the remaining cells 4 correspond to the cells 4 in which the plugging portions 8 are not provided on the one end face 2a side. As a result, the one end surface 2a (inflow side end surface 3a) and the other end surface 2b (discharging side end surface 3b) are plugged according to a predetermined arrangement standard. Here, the arrangement standard of the plugging portions 8 is not limited to the checkerboard pattern, and can be set arbitrarily.

  In addition, the individual cells do not have to have the same shape, and a plugged honeycomb structure formed by combining cells of two different sizes in which adjacent cells have different sizes may be used. Further, the shape of the cells is not limited to the regular quadrangular shape shown in FIG. 1 and the like, and may be cells having other polygonal shapes such as hexagonal shape and octagonal shape.

  Here, the material for forming the plugged portion 8 is not particularly limited, and a known plugging material combining a ceramic material, alcohol, an organic binder and the like can be used. Further, the known ceramic materials include, for example, a group consisting of silicon carbide, silicon-silicon carbide based composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite based composite material, lithium aluminum silicate, and aluminum titanate. At least one selected from the above may be used. These may be selected according to the raw material of the partition walls forming the plugged honeycomb structure and the like.

  By providing the plugging portion 8 on the honeycomb substrate 6 of the plugged honeycomb structure 1 as described above, the plugged honeycomb structure 1 can be used as an exhaust gas purifying device, a particulate collection filter, or the like. Can be used as a configuration. When a fluid F such as exhaust gas is flown into the plugged honeycomb structure 1 from the inflow side end face 3a toward the discharge side end face 3b, the inside of the cell 4 in which the opening 7a of the inflow side end face 3a is opened. The fluid F that has flown in (entered) into the exhaust gas tends to flow along the honeycomb axial direction A toward the discharge-side end surface 3b.

  However, the cells 4 in the opening 7b of the discharge side end surface 3b facing the inflow side end surface 3a are plugged by the plugging portion 8. Therefore, the behavior of the flow of the fluid F is regulated. Therefore, the inflowing fluid F passes through the porous partition wall 5 and is discharged to the outside of the plugged honeycomb structure 1 from the openings 7b of the cells 4 opened on the discharge side end surface 3b (FIGS. 3 and 4). (See fluid F ′ indicated by the chain double-dashed line in FIG.

  That is, even if the fluid F flows in from the cells 4 having the opening on the inflow side end face 3a, the fluid F is directly transferred to the outside of the plugged honeycomb structure 1 by the plugging portion 8 provided on the discharge side end face 3b. It is never discharged. Therefore, the behavior of the flow of the fluid F is regulated, and a large amount of the particulate matter 10 contained in the fluid F is deposited in the vicinity of the discharge-side end surface 3b where the plugging portion 8 is provided (see FIG. 3). Even when the fluid F passes through the porous partition wall 5, the particulate matter 10 is collected on the partition wall surface and inside the partition wall. As a result, the purification process for removing the particulate matter 10 contained in the fluid F is performed, and the purification fluid C can be discharged from the discharge-side end surface 3b.

  The partition walls 5 forming the plugged honeycomb structure 1 of the present embodiment can be made of substantially the same ceramic material as that of the plugging portion 8 described above. More specifically, the partition wall 5 includes, as a raw material 13, a particulate base material 11 and a binding material 12 that binds the base materials 11 to each other and has a lower melting point than the base material 11 (see FIG. 2).

  An example of the ceramic material used for the base material 11 and the binding material 12 constituting the partition wall 5 is one or more kinds selected from the group including cordierite, alumina, mullite, silicon nitride, silicon carbide, and aluminum titanate. Can be used. In the plugged honeycomb structure 1 of the present embodiment, unless otherwise specified, silicon carbide (SiC) particles are used as the base material 11 and cordierite is used as the binder 12. Assumed to be performed.

  Here, the binder 12 used for the partition wall 5 has a lower melting point than the base material 11. As a result, when the plugged honeycomb structure 1 is exposed to a high temperature, the binder 12 melts earlier than the base material 11. This makes it possible to easily form the circular cells 9 defined by the arcuate partition walls 5a from the polygonal cells 14 (details will be described later).

  Here, in consideration of the melting point of a general ceramic material, the melting point of the binder 12 is preferably at least 1100 ° C. or higher. As a result, the melting point of the particulate base material 11 is naturally 1100 ° C. or higher, and the possibility of melting the base material 11 is reduced. As a result, a part of the binder 12 contained in the raw material 13 is melted by the fluid F containing the particulate matter 10, which facilitates the formation of the circular cells 9 in the plugged honeycomb structure 1 of the present embodiment. (Details will be described later.)

  Further, the particle diameter of the base material 11 used for the partition walls 5 is in the range of 5 μm to 60 μm. Here, when the particle diameter of the base material 11 is less than 5 μm, the strength of the base material 11 itself is often low. As a result, the heat resistance and thermal shock resistance of the plugged honeycomb structure 1 itself using these base materials 11 become low, and cracks and the like during use are likely to occur. Therefore, the particle size of the base material 11 needs to be at least 5 μm or more.

  On the other hand, when the particle diameter of the base material 11 is larger than 60 μm, the binder 12 has a lower melting point than the base material 11, and the plugged honeycomb structure 1 is exposed to a high temperature equal to or higher than the melting point of the binder 12. Even in this case, the particulate base materials 11 interfere with each other and the partition wall 5 is less likely to be transformed into the arc partition wall 5a. Therefore, the circular cells 9 may not be easily formed (details will be described later). Therefore, the particle size of the base material 11 is regulated within the above range.

  In addition, the mass ratio of the binder 12 with respect to the total mass of the raw materials of the base material 11 and the binder 12 that form the partition wall 5 is defined in the range of 22 mass% to 45 mass%. Here, when the mass ratio of the binder 12 is less than 22 mass%, the plugged honeycomb structure 1 having the partition walls 5 including the binder 12 is exposed to a high temperature and is equal to or higher than the melting point of the binder 12 (for example, 1100). Even if the temperature is higher than or equal to 0 ° C.), the partition wall 5 is less likely to be transformed into the arc-shaped partition wall 5a because the proportion of the binder 12 is small. Therefore, the circular cells 9 may not be easily formed (details will be described later). Therefore, the mass ratio of the binder 12 is regulated within the above range.

  Further, the plugged honeycomb structure 1 of the present embodiment is set so that the radius of curvature R at the partition wall intersection portion 15 of the arc partition wall 5a that defines and forms the circular cells 9 is 250 μm or more. Here, when the curvature radius R of the partition wall intersection portion 15 is less than 250 μm, the thermal stress applied to the partition wall intersection portion 15 where the plurality of partition walls 5 and 5a intersect is concentrated, and the dispersion effect of the circular arc partition wall 5a becomes weak. Therefore, thermal stress concentration occurs similarly to the lattice-shaped partition wall, and cracks are likely to occur. Therefore, the curvature radius R at the partition wall intersection portion 15 of the arc partition wall 5a is defined to be 250 μm or more.

2. Method for forming plugged honeycomb structure (deformation of circular cell)
The plugged honeycomb structure 1 of the present embodiment is formed by the following forming method. The method for forming the plugged honeycomb structure 1 of the present invention is not limited to this, and may be formed by previously having the circular cells 9 inside.

  The plugged honeycomb structure 1 of this embodiment is formed by using the polygonal plugged honeycomb structure 20 as a starting material. Here, the polygonal plugged honeycomb structure 20 includes, as shown in FIG. 3, a honeycomb base material 6 having partition walls 5 partitioning and forming a plurality of polygonal cells 14, and one end surface 2 a of the honeycomb base material 6. And the other end surface 2b is plugged according to a predetermined arrangement standard. That is, the polygonal plugged honeycomb structure 20 is a well-known one that has been conventionally used in an exhaust gas purification apparatus and the like, and the plugged cell of the present embodiment is that it does not have the circular cells 9 therein. It is different from the honeycomb structure 1.

  The configuration of the partition walls 5 of the polygonal plugged honeycomb structure 20 (the base material 11 and the binder 12), the fact that the binder 12 has a lower melting point than the base material 11, the particle diameter of the base material 11, and the raw material 13 The mass ratio of the binder 12 to the total mass, the melting point of the binder, the ceramic material used for the base material 11 and the binder 12, and the like are the same as those of the plugged honeycomb structure 1 of the present embodiment already described. is there.

  In the polygonal plugged honeycomb structure 20, the same components as those of the plugged honeycomb structure 1 of the present embodiment are designated by the same reference numerals and the description thereof will be omitted. A method for manufacturing the polygonal plugged honeycomb structure 20 (conventional plugged honeycomb structure) is well known and will not be described here.

  With the polygonal plugged honeycomb structure 20 incorporated in an exhaust gas purifying apparatus or the like, from one end surface 2a (inflow side end surface 3a) of the honeycomb substrate 6 to the other end surface 2b (exhaust side end surface 3b). The fluid F is caused to flow in (fluid inflow step: see FIGS. 2 and 3). As a result, the particulate matter 10 contained in the fluid F is collected inside the cells 16 of the polygonal plugged honeycomb structure 20 (particulate matter collecting step). Note that the collection of the particulate matter 10 is the same as the collection of the particulate matter by the plugged honeycomb structure 1 and has already been described, so description thereof will be omitted here.

  The particulate matter 10 is deposited in the cell interior 16 by the particulate matter collection step. The fluid F is exhaust gas or the like discharged from the diesel engine and has a high temperature. The binder 12 has a low melting point with respect to the base material 11 forming the partition walls 5, the particle size of the base material 11 is in the range of 5 μm to 60 μm, and the mass ratio of the binder 12 to the total mass of the raw materials 13 is 22. It is in the range of mass% to 45 mass%.

  By exposing the polygonal plugged honeycomb structure 20 to a temperature equal to or higher than the melting point of the bonding material 12 by the high temperature fluid F that satisfies these conditions and is in the regeneration process, at least a part of the polygonal cells 14 is partitioned and formed. Part of the binding material 12 that constitutes the partition wall 5 is melted. As a result, a part of the lattice-shaped partition wall 5 is transformed into a curved arc partition wall 5a. As a result, the polygonal cell 14 is transformed into the circular cell 9 in which at least a part of the polygonal cell 5a is partitioned and formed (the circular cell transformation step).

  That is, the binder 12 having a lower melting point than the base material 11 is used, and the high temperature fluid F containing the particulate matter 10 flows in under a predetermined condition, so that a part of the polygonal cell 14 is transferred to the circular cell 9. It can be transformed. As a result, it is possible to disperse the thermal stress concentration particularly at the partition wall intersection portion 15 and suppress the occurrence of defects such as cracks.

  Further, as compared with a plugged honeycomb structure in which circular cells are formed in advance, the cell density does not become lower and the pressure loss performance after the deposition of the particulate matter 10 does not decrease, so the above-mentioned forming method Are particularly suitable. It should be noted that depending on the intended use and the like, a sufficient effect can be obtained even with a plugged honeycomb structure having circular cells formed in advance.

  Examples of the plugged honeycomb structure and the method for forming the plugged honeycomb structure of the present invention will be described below, but the plugged honeycomb structure of the present invention is not limited thereto.

1. Plugged honeycomb structure (Polygonal cell plugged honeycomb structure)
Based on the above-described method for forming a plugged honeycomb structure, the plugged honeycomb structures of Examples 1 to 5 and Comparative Examples 1 to 5 are created from well-known polygonal cell plugged honeycomb structures created in advance. did. Here, the cell shapes of the polygonal cell plugged honeycomb structure before forming the circular cells were all quadrangular, and the honeycomb diameter was 143.8 mm and the honeycomb length was 152.4 mm. .. In the cell shape of the polygonal cell plugged honeycomb structure before forming the plugged honeycomb structures of Examples 1 to 5 and Comparative Examples 1 to 5, the particle diameter of the base material forming the partition wall, and the partition wall Table 1 below summarizes the mass ratios of the binders contained to the total mass of the raw materials. In addition, in the plugged honeycomb structures (polygonal plugged honeycomb structures) of Examples 1 to 5 and Comparative Examples 1 to 5, particles of silicon carbide (SiC) were used as a base material, while the binder was used. Is used as a cordierite. Here, the melting point of silicon carbide (SiC) used as the base material is 2730 ° C., while the melting point of cordierite used as the binder is 1400 ° C. Further, Comparative Example 1 uses cordierite as the base material and does not contain a binder. Regarding the melting points of the base material and the binder, it is possible to specify the crystal phase of each component by performing X-ray diffraction measurement using an X-ray analyzer (details will be described later). After the crystal phase is specified, measurement may be performed by a known melting point measuring device, or the crystal phase may be specified based on the specified crystal phase with reference to known literature values.

2. Measurement of Particle Size of Substrate The particle size of the substrate constituting the partition wall was measured by electron microscope observation as follows. Specifically, from the plugged honeycomb structures of Examples 1 to 5 and Comparative Examples 1 to 5, a cube of 5 mm square for electron microscope observation is cut out. At this time, the above cutting is performed so that the cross section of the partition wall appears on the surface of the cut cubic shape. Next, the obtained sample is embedded in a resin and hardened, and then the surface is polished. After that, an SEM photograph (scanning electron microscope photograph) is taken at a magnification of 400 times for a portion where the partition wall cross section appears on the polished sample surface. The SEM image of the captured SEM photograph is image-processed to identify the base material and the binder in the SEM image. In addition, as a specific method of identification, for example, in the SEM image placed under the image analysis, the position where the base material is present and the position where the binder is present are color-coded. Here, SU9000 (manufactured by Hitachi High-Tech Co., Ltd.) was used as a scanning electron microscope for capturing an SEM photograph. Further, the imaged SEM image was subjected to image analysis using an image processing system XG (manufactured by Keyence Corporation).

  After the base material and the binder are identified by the image analysis, the particle size of the base material is calculated. The particle size of the substrate means the particle size (sphere equivalent diameter) obtained by converting the substrate into spherical particles. First, the particle area (cross-sectional area) of the base material on the captured SEM image is measured by image processing. Next, a particle diameter converted into granular particles having the same area as the measured particle area was calculated and used as the particle diameter of the base material.

3. Calculation of Mass Ratio The mass ratio of the binder contained in the partition wall to the total mass of the raw materials was calculated by the following method. First, an X-ray diffraction pattern (a product name: RINT, manufactured by Rigaku Denki Co., Ltd.) was used to obtain an X-ray diffraction pattern of the material forming the partition wall. At this time, the conditions of the X-ray diffraction measurement were a CuKα radiation source, 50 kV, 300 mA, 2θ = 10 to 60 °. Then, a simple quantitative analysis was performed to calculate the mass ratios of the crystal phases of the respective constituents. In addition, for the simple quantitative analysis, the RIR (Reference Intensity Ratio) method was used, and the obtained X-ray diffraction data was analyzed to quantify each component. X-ray data analysis software (trade name: JADE7, manufactured by MDI) was used to analyze the X-ray diffraction data.

4. Formation of circular cells (accumulation of soot)
The exhaust gas purifying apparatus equipped with the polygonal plugged honeycomb structures of Examples 1 to 5 and Comparative Examples 1 to 5 adjusted to the particle diameter of the base material and the mass ratio of the binder shown in Table 1 was exhausted. The exhaust gas (fluid) is attached to the exhaust system of a passenger vehicle equipped with a 2.0-liter engine and the exhaust gas (fluid) is made to flow from the inflow side end face to the exhaust side end face (fluid inflow process) to form a polygonal plugged honeycomb structure. Soot (particulate matter) was deposited inside the cell (particulate matter collecting step). At this time, the amount of soot deposited was such that the weight per unit volume of the polygonal plugged honeycomb structure was 12 g / L. In the process according to the internal cell soot is sedimentary, that the temperature of the partition wall reaches a temperature above the melting point of the binder, at least a portion of the polygon cells, an arc partition wall portion of the partition wall exhibits an arcuate It is transformed and transformed into a circular cell such as a circular shape (circular cell transformation step). As a result, a plugged honeycomb structure having circular cells of Examples 1 to 5 is formed.

5. Regeneration Treatment A regeneration treatment for removing deposited soot is performed on Examples 1 to 5 and Comparative Examples 1 to 5 in which 12 g of soot per unit volume of the plugged honeycomb structure is deposited. Specifically, similar to the accumulation of soot (formation of circular cells), with an exhaust gas purifying device attached to the exhaust system of a passenger car equipped with an engine having a displacement of 2.0 liters, under conditions of 2000 rpm / 80 Nm. Rotate the engine. Furthermore, the temperature of the exhaust gas at a position 20 mm before the inflow side end surface of the plugged honeycomb structure was measured using a sheath thermocouple (K type, Φ0.5), and the fuel injection amount was adjusted to 650. Raise the temperature to ℃. After that, the operation of the engine was switched to an idle state (800 rpm / 12 Nm) to regenerate the soot accumulated inside the cell. At this time, the temperature at a position 10 mm upstream from the discharge-side end surface of the plugged honeycomb structure was measured using a sheath thermocouple (same as above). Among the temperatures measured by the sheath thermocouple, the value showing the highest temperature was defined as the maximum temperature during the regeneration treatment (see Table 1).

6. Change in radius of curvature before collection and after regeneration treatment Polygonal plugged honeycomb structure before collecting soot of Examples 1 to 5 and Comparative Examples 1 to 5 and plugged honeycomb structure after regeneration treatment With respect to each of the above, the plugging portion is removed from the discharge side end surface, and cut as a cutting surface orthogonal to the honeycomb axial direction (see the orthogonal surface CF in FIG. 1 and the like). The radius of curvature R is measured at four measurement points P1, P2, P3, P4 (see FIG. 5) of the partition wall intersection portion of an arbitrary cell on the cut surface, and the average radius of curvature R of the partition wall intersection portion in one cell is calculated. Calculated. The same calculation process as above was performed on any five cells, and the average value of the radii of curvature R in the five cells was taken as the radius of curvature R of the partition wall intersection point (see Table 1). Here, the radius of curvature R was measured by using an enlarged image of the cut surface taken under the condition of a magnification of 20 under the observation of the cut surface under an optical microscope or under an electron microscope. It is also possible to analyze the image as needed.

  In the case of a circular cell, the radius of curvature R is measured at arbitrary four measurement points P1 ′, P2 ′, P3 ′, P4 ′ (see FIG. 5) with respect to the deformed point, and similarly, the partition wall intersection point in one cell is measured. After calculating the radius of curvature R of the deformation of the part, measurement was performed on any maximum of 5 cells, and the average value was calculated (see Table 1). Here, in order to simplify the illustration, FIG. 5 exemplifies measurement points P1 and the like at the partition wall intersections of the cell before collecting soot and measurement points P1 ′ and the like at the partition wall intersections of the circular cell after the regeneration treatment. However, the measurement points P1, P1 ′, etc. are set on the cut surfaces before the soot collection and after the regeneration processing, respectively.

7. Ratio of the number of circular cells The total number of cells in an arbitrary range in the cut surface (see 6 above) of the plugged honeycomb structure subjected to the regeneration treatment is visually measured, and the circular cells occupy the total number of cells. Was visually measured and the ratio was calculated (see Table 1). The measurement of the total number of cells and the number of circular cells used the images of the above-mentioned 6 cut surfaces.

8. Measurement of the number of cracked partition walls and determination of crack generation The number of cracked partition walls of the partition walls was visually measured on the cut surface of the plugged honeycomb structure subjected to the regeneration treatment (see above 6 and 7) (Table 1 reference). For the measurement of the number of cracked partition walls, the image of the cut surface of 6 was used. Here, the determination of crack generation is based on the plugged honeycomb structure of Comparative Example 1 that does not use a binder, and is compared with 24 locations that are the number of cracked partition walls in Comparative Example 1, and half of Comparative Example 1 The case where the above reduction is recognized is "A", the case where the reduction is recognized at three or more locations is "B", the case where the number of cracking partition walls is the same as Comparative Example 1 (± 2 locations) is "C", the comparison is made. A case where an increase in three or more places was recognized as compared with Example 1 was evaluated as “D” and judged.

9. Summary of Examples 9.1 Particle Size of Base Material As shown in Table 1, all of the plugged honeycomb structures of Examples 1 to 5 in which the particle size of the base material is in the range of 5 μm to 60 μm are The formation of circular cells was observed inside. On the other hand, in the plugged honeycomb structure of Comparative Example 2 in which the particle diameter of the base material is less than 5 μm (particle diameter of the base material = 4 μm), although the formation of circular cells is recognized, the number of crack generation partition walls is large at 35 locations. Become. That is, it was confirmed that the strength of the plugged honeycomb structure was lowered.

On the other hand, in the plugged honeycomb structure of Comparative Example 3 in which the particle size of the base material was 60 μm or more (particle size of the base material = 62 μm), formation of circular cells was not observed. The particles of the base material interfere with each other to suppress deformation into circular cells. This tendency was also confirmed in Examples 2 and 4, and when the substrate particle diameter was 60 μm, the ratio of the number of circular cells to the total number of cells was lower than that in the other Examples 1, 3, and 5. (Example 2 = 3%, Example 4 = 11%). Therefore, it was shown that the particle size of the substrate is preferably in the range of 5 μm to 60 μm in the present invention.

9.2 Mass Ratio of Binders In all of the plugged honeycomb structures of Examples 1 to 5 in which the mass ratio of the binder is in the range of 22% by mass to 45% by mass, the formation of circular cells is recognized therein. Was given. On the other hand, in the plugged honeycomb structure of Comparative Example 4 (= 21% by mass) in which the mass ratio of the binder was less than 22% by mass, formation of circular cells was not observed. Similarly, in Comparative Example 1 containing no binder (= 0% by mass), formation of circular cells was not observed. That is, in order to form the plugged honeycomb structure having the circular cells of the present invention, it was confirmed that the binder was indispensable in addition to the base material as the raw material.

  On the other hand, in the plugged honeycomb structure of Comparative Example 5 in which the mass ratio of the binder was 45 mass% or more (mass ratio = 46.5 mass%), although the formation of circular cells was recognized, the cracked partition wall locations were 31. There are many places. That is, it was confirmed that the strength of the plugged honeycomb structure was lowered. Therefore, it was shown that the mass ratio of the binder is preferably in the range of 22 mass% to 45 mass% in the present invention.

9.3 Change in radius of curvature The radius of curvature of the partition wall intersection before collection was 59 to 61 μm in Examples 1 to 5 and Comparative Examples 1 to 5, whereas a circular cell was formed. It was confirmed that each of the plugged honeycomb structures after the regeneration treatment had a radius of curvature of 250 μm or more.

9.4 Ratio of Number of Circular Cells As shown in Table 1, in the plugged honeycomb structures of Examples 3 to 5 in which the ratio of the number of circular cells exceeds 10%, the number of cracked partition walls is determined in Comparative Example 1. It was found to be reduced to more than the lower half than the reference number. That is, it was shown that when the ratio of the number of circular cells to the total number of cells is 10% or more, the effect of alleviating the thermal stress concentration at the partition wall intersections becomes particularly large.

  As described above, according to the plugged honeycomb structure of the present invention, by having the circular cells inside, it is possible to alleviate the thermal stress concentration and suppress the occurrence of cracks in the partition walls. In particular, the particle diameter of the base material that constitutes the partition wall, the ratio of the binder, and the use of a binder having a melting point lower than that of the base material make it possible to obtain a circular shape when purifying a fluid that traps particulate matter. The cells can be formed relatively easily. As a result, the strength of the plugged honeycomb structure can be improved as compared with the conventional polygonal cells that are partitioned and formed by the lattice-shaped partition walls.

  In particular, since a part of the cells is not configured in advance as circular cells, it is possible to prevent problems such as a decrease in cell density from the beginning before collection and an increase in pressure loss.

  INDUSTRIAL APPLICABILITY The plugged honeycomb structure of the present invention is particularly beneficially used in applications such as an exhaust gas purification treatment device that purifies particulate matter such as fine particles contained in a fluid such as exhaust gas discharged from a diesel engine or the like. Therefore, the method for forming the plugged honeycomb structure can preferably form the plugged honeycomb structure used in the exhaust gas purifying apparatus and the like.

1: Plugged honeycomb structure, 2a: One end face, 2b: The other end face, 3a: Inflow side end face, 3b: Discharge side end face, 4: Cell, 5: Partition wall, 5a: Arc partition wall, 6: Honeycomb substrate Material, 7a, 7b: Opening part, 8: Plugging part, 9: Circular cell, 10: Particulate material, 11: Base material, 12: Binder, 13: Raw material, 14: Polygonal cell, 15: Partition wall Intersection points, 16: inside of cell, 20: polygonal plugged honeycomb structure, A: honeycomb axial direction, C: purification fluid, CF: orthogonal plane, F, F ': fluid, P1, P1', P2, P2. ', P3, P3', P4, P4 ': measurement location, R: radius of curvature.

Claims (8)

From one end face to the other end face, a honeycomb substrate having a porous partition wall partitioning and forming a plurality of cells to be a fluid flow path,
While plugging the cells on the one end surface of the honeycomb substrate according to a predetermined disposition standard, a plugging portion that plugs each of the remaining cells on the other end surface, respectively,
A plugged honeycomb structure for collecting particulate matter contained in the fluid flowing from an inflow side end surface which is the one end surface of the honeycomb substrate toward an exhaust side end surface which is the other end surface, ,
The partition wall is
A particulate base material, and binding the base materials to each other, and including a binder having a lower melting point than the base material as a raw material,
The particle size of the substrate is
5 μm to 60 μm,
The mass ratio of the binder to the total mass of the raw materials including the base material and the binder,
22 mass% to 45 mass%,
The cell is
By an arc barrier wall at least a part of the partition wall exhibits an arcuate, possess a part circular, elliptical or circular cells divided formed in a semicircular shape,
The radius of curvature at the partition wall intersection portion of the arc partition wall partitioning and forming the circular cell is
A plugged honeycomb structure having a size of 250 μm or more . The ratio of the number of circular cells of the circular cells to the total number of cells of the cells on the orthogonal surface orthogonal to the honeycomb axis direction of the plugged honeycomb structure is:
The plugged honeycomb structure according to claim 1, which is 10% or more. The circular cell is
The plugged honeycomb structure according to claim 1 or 2, which is located near the plugging portion provided on the discharge-side end surface.   Having a plurality of polygonal polygonal cells defined by the partition walls, the fluid is caused to flow from the inflow side end surface of the polygonal plugged honeycomb structure before capturing the particulate matter, and the particulate matter The plugging according to any one of claims 1 to 3, further comprising the circular cells formed by deforming the polygonal cells by exposing the binder to a temperature equal to or higher than a melting point after collecting the substance. Honeycomb structure. The melting point of the binder is
The plugged honeycomb structure according to any one of claims 1 to 4, which has a temperature of 1100 ° C or higher. The base material and the binder are
The plugged honeycomb structure according to any one of claims 1 to 5, which is one or more ceramic materials selected from the group including cordierite, alumina, mullite, silicon nitride, silicon carbide, and aluminum titanate. .. The base material is
Is the silicon carbide,
The binder is
The plugged honeycomb structure according to claim 6 , which is the cordierite . A method for forming a plugged honeycomb structure according to any one of claims 1 to 7,
A honeycomb substrate having porous partition walls that form a plurality of polygonal cells that serve as fluid channels and extend from one end face to the other end face, and the polygon on the one end face of the honeycomb substrate. While plugging the cells according to a predetermined arrangement standard, the polygonal plugged honeycomb structure having plugged portions that plugged the remaining polygonal cells on the other end face, respectively, the one A fluid inflow step of inflowing the fluid from the inflow side end surface which is the end surface of the fluid toward the discharge side end surface which is the other end surface,
Particulate matter contained in the fluid, a particulate matter collecting step of depositing and collecting inside the cells of the polygonal cell in which the plugging portion is formed on the discharge side end surface,
After the particulate matter is deposited inside the cell by the particulate matter collecting step, the polygonal plugged honeycomb structure is exposed to a temperature equal to or higher than the melting point of the binder, whereby the polygonal cell A plugged honeycomb structure having at least a part of which is a circular cell deformation step in which the partition wall is deformed into an arcuate partition wall having an arc shape, and is transformed into a circular cell having a circular shape, an elliptical shape, or a semicircular shape. How to form a body.

Images